U.S. patent application number 16/215971 was filed with the patent office on 2020-06-11 for transferring a writable data set to a cloud service.
This patent application is currently assigned to EMC IP Holding Company LLC. The applicant listed for this patent is EMC IP Holding Company LLC. Invention is credited to Douglas E. LeCrone, Bruce A. Pocock.
Application Number | 20200183801 16/215971 |
Document ID | / |
Family ID | 70971927 |
Filed Date | 2020-06-11 |
United States Patent
Application |
20200183801 |
Kind Code |
A1 |
LeCrone; Douglas E. ; et
al. |
June 11, 2020 |
TRANSFERRING A WRITABLE DATA SET TO A CLOUD SERVICE
Abstract
Transferring data from a storage device to cloud service
includes initiating a snapshot of the data, accessing each block of
the data corresponding to the snapshot to transfer each block to
the cloud service, and terminating the snapshot after all of the
blocks have been transferred to the cloud service. At least some
blocks of the storage device that are modified after initiating the
snapshot may be copied from the storage device to a storage pool
prior to modification. Only a first modification of a particular
one of the blocks of the storage device may cause the particular
one of the blocks to be copied to the storage pool. Accessing each
block of the data may include accessing blocks of the storage pool.
Modifying a particular one of the blocks of the storage device may
include modifying a corresponding block of a storage pool.
Inventors: |
LeCrone; Douglas E.;
(Hopkinton, MA) ; Pocock; Bruce A.; (Hoschton,
GA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EMC IP Holding Company LLC |
Hopkinton |
MA |
US |
|
|
Assignee: |
EMC IP Holding Company LLC
Hopkinton
MA
|
Family ID: |
70971927 |
Appl. No.: |
16/215971 |
Filed: |
December 11, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06F 3/0607 20130101;
G06F 3/067 20130101; G06F 11/2082 20130101; G06F 3/064 20130101;
G06F 2201/84 20130101; G06F 11/2097 20130101; G06F 11/2094
20130101; G06F 3/0644 20130101; G06F 3/0647 20130101; G06F 3/065
20130101; G06F 3/0617 20130101 |
International
Class: |
G06F 11/20 20060101
G06F011/20; G06F 3/06 20060101 G06F003/06 |
Claims
1. A method of transferring data from a storage device to cloud
service, comprising: initiating a snapshot of the data at the
storage device; accessing each block of the data corresponding to
the snapshot to transfer each block to the cloud service that is
separate from the storage device; and terminating the snapshot at
the storage device after all of the blocks have been transferred
from the storage device to the cloud service.
2. A method, according to claim 1, wherein at least some blocks of
the storage device that are modified after initiating the snapshot
are copied from the storage device to a storage pool prior to
modification.
3. A method, according to claim 2, wherein only a first
modification of a particular one of the blocks of the storage
device causes the particular one of the blocks to be copied to the
storage pool.
4. A method, according to claim 2, wherein accessing each block of
the data includes accessing blocks of the storage pool.
5. A method, according to claim 1, wherein modifying a particular
one of the blocks of the storage device includes modifying a
corresponding block of a storage pool.
6. A method, according to claim 5, wherein accessing each block of
the data includes accessing only blocks on the storage device.
7. A method, according to claim 1, wherein prior to initiating the
snapshot, modifications directed toward the storage device cause
blocks of the storage device to be modified.
8. A method, according to claim 1, wherein following terminating
the snapshot, modifications directed toward the storage device
cause blocks of the storage device to be modified.
9. A method, according to claim 1, wherein the cloud service is
provided by cloud storage.
10. A method, according to claim 9, wherein the cloud storage is
publicly available.
11. A non-transitory computer readable medium containing software
that transfers data from a storage device to cloud service, the
software comprising: executable code that initiates a snapshot of
the data at the storage device; executable code that accesses each
block of the data corresponding to the snapshot to transfer each
block to the cloud service that is separate from the storage
device; and executable code that terminates the snapshot at the
storage device after all of the blocks have been transferred from
the storage device to the cloud service.
12. A non-transitory computer readable medium, according to claim
11, wherein at least some blocks of the storage device that are
modified after initiating the snapshot are copied from the storage
device to a storage pool prior to modification.
13. A non-transitory computer readable medium, according to claim
12, wherein only a first modification of a particular one of the
blocks of the storage device causes the particular one of the
blocks to be copied to the storage pool.
14. A non-transitory computer readable medium, according to claim
12, wherein accessing each block of the data includes accessing
blocks of the storage pool.
15. A non-transitory computer readable medium, according to claim
1, wherein modifying a particular one of the blocks of the storage
device includes modifying a corresponding block of a storage
pool.
16. A non-transitory computer readable medium, according to claim
15, wherein accessing each block of the data includes accessing
only blocks on the storage device.
17. A non-transitory computer readable medium, according to claim
11, wherein prior to initiating the snapshot, modifications
directed toward the storage device cause blocks of the storage
device to be modified.
18. A non-transitory computer readable medium, according to claim
11, wherein following terminating the snapshot, modifications
directed toward the storage device cause blocks of the storage
device to be modified.
19. A non-transitory computer readable medium, according to claim
11, wherein the cloud service is provided by cloud storage.
20. A method, according to claim 19, wherein the cloud storage is
publicly available.
Description
TECHNICAL FIELD
[0001] This application relates to the field of computer systems
and storage devices therefor and, more particularly, to the field
of storage access and I/O operations for data being transferred to
a cloud service.
BACKGROUND OF THE INVENTION
[0002] Host processor systems may store and retrieve data using a
storage device containing a plurality of host interface units (I/O
modules), disk drives, and disk interface units (disk adapters).
The host systems access the storage device through a plurality of
channels provided therewith. Host systems provide data and access
control information through the channels to the storage device and
the storage device provides data to the host systems also through
the channels. The host systems do not address the disk drives of
the storage device directly, but rather, access what appears to the
host systems as a plurality of logical disk units. The logical disk
units may or may not correspond to any one of the actual disk
drives. Allowing multiple host systems to access the single storage
device unit allows the host systems to share data stored
therein.
[0003] In some cases, it is desirable to use a cloud service to
store and retrieve data. Cloud services generally provide on-demand
service, broad network access, resource pooling, and rapid
elasticity or expansion, and thus may be beneficial for many
storage applications. However, transferring a data set from a
storage device to a cloud service may require that the source data
set not be modified at the storage device during the transfer
process if it is desirable to maintain data integrity of the
resulting replica of the data set at the cloud service. For
example, if a data set includes the blocks A, B, and C at the time
that a transfer to a cloud service is initiated, and the data set
is modified after block A has been transferred but before block C
has been transferred to become A', B, and C', then the data set at
the cloud service will become A, B, and C', which is inconsistent
because it contains A and C' together rather than A and C or A' and
C'.
[0004] One way to address this issue is to prevent modification of
a data set while the data set is being transferred to a cloud
service. Thus, in the example above, A, B, C would be transferred
to the cloud service prior to writing to the data set. While this
solution may address issues of data inconsistency of data
transferred to a cloud service, it requires preventing modification
of a data set while data is being transferred to the cloud service.
In some instances, this may be unacceptable, especially in cases
where it takes a significant amount of time to transfer the data
set to the cloud service.
[0005] Accordingly, it is desirable to be able to modify a data set
while the data set is being transferred to a cloud service in a
manner that maintains integrity of the resultant replica data set
at the cloud service.
SUMMARY OF THE INVENTION
[0006] According to the system described herein, transferring data
from a storage device to cloud service includes initiating a
snapshot of the data, accessing each block of the data
corresponding to the snapshot to transfer each block to the cloud
service, and terminating the snapshot after all of the blocks have
been transferred to the cloud service. At least some blocks of the
storage device that are modified after initiating the snapshot may
be copied from the storage device to a storage pool prior to
modification. Only a first modification of a particular one of the
blocks of the storage device may cause the particular one of the
blocks to be copied to the storage pool. Accessing each block of
the data may include accessing blocks of the storage pool.
Modifying a particular one of the blocks of the storage device may
include modifying a corresponding block of a storage pool.
Accessing each block of the data may include accessing only blocks
on the storage device. Prior to initiating the snapshot,
modifications directed toward the storage device may cause blocks
of the storage device to be modified. Following terminating the
snapshot, modifications directed toward the storage device may
cause blocks of the storage device to be modified. The cloud
service may be provided by cloud storage. The cloud storage may be
publicly available.
[0007] According further to the system described herein, a
non-transitory computer readable medium contains software that
transfers data from a storage device to cloud service. The software
includes executable code that initiates a snapshot of the data,
executable code that accesses each block of the data corresponding
to the snapshot to transfer each block to the cloud service, and
executable code that terminates the snapshot after all of the
blocks have been transferred to the cloud service. At least some
blocks of the storage device that are modified after initiating the
snapshot may be copied from the storage device to a storage pool
prior to modification. Only a first modification of a particular
one of the blocks of the storage device may cause the particular
one of the blocks to be copied to the storage pool. Accessing each
block of the data may include accessing blocks of the storage pool.
Modifying a particular one of the blocks of the storage device may
include modifying a corresponding block of a storage pool.
Accessing each block of the data may include accessing only blocks
on the storage device. Prior to initiating the snapshot,
modifications directed toward the storage device may cause blocks
of the storage device to be modified. Following terminating the
snapshot, modifications directed toward the storage device may
cause blocks of the storage device to be modified. The cloud
service may be provided by cloud storage. The cloud storage may be
publicly available.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Embodiments of the system are described with reference to
the several figures of the drawings, noted as follows.
[0009] FIG. 1 is a schematic illustration of a storage system
showing a relationship between a host and a storage device that may
be used in connection with an embodiment of the system described
herein.
[0010] FIG. 2 is a schematic diagram illustrating an embodiment of
the storage device where each of a plurality of directors are
coupled to the memory.
[0011] FIG. 3 is a schematic illustration showing a system with a
host, a data storage device, and a cloud service according to an
embodiment of the system described herein.
[0012] FIG. 4 is a schematic illustration showing a data set,
metadata, and a storage pool of a data storage device according to
an embodiment of the system described herein.
[0013] FIG. 5 is a flow diagram illustrating processing performed
in connection with a data set being modifiable while being
transferred to a cloud service according to an embodiment of the
system described herein.
[0014] FIG. 6 is a flow diagram illustrating processing performed
in connection with transferring modifiable data to a cloud service
according to an embodiment of the system described herein.
[0015] FIG. 7 is a flow diagram illustrating processing performed
in connection with handling write operations to a dataset while a
snapshot is active according to an embodiment of the system
described herein.
[0016] FIG. 8 is a flow diagram illustrating processing performed
in connection with handling write operations to a dataset while a
snapshot is active according to an alternative embodiment of the
system described herein.
DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS
[0017] FIG. 1 is a schematic illustration of a storage system 20
showing a relationship between a host 22 and a storage device 24
that may be used in connection with an embodiment of the system
described herein. The host 22 may be a computer running Linux, z/OS
or some other appropriate operating system. In an embodiment, the
storage device 24 may be a Symmetrix or VMAX storage system
produced by Dell EMC of Hopkinton, Mass.; however, the system
described herein may operate with other appropriate types of
storage devices. Also illustrated is another (remote) storage
device 26 that may be similar to, or different from, the storage
device 24 and may, in various embodiments, be coupled to the
storage device 24, for example, via a network. The host 22 reads
and writes data from and to the storage device 24 via an HA 28
(host adapter), which facilitates an interface between the host 22
and the storage device 24. Although the diagram 20 only shows one
host 22 and one HA 28, it will be appreciated by one of ordinary
skill in the art that multiple host adaptors (possibly of different
configurations) may be used and that one or more HAs may have one
or more hosts coupled thereto.
[0018] In an embodiment of the system described herein, in various
operations and scenarios, data from the storage device 24 may be
copied to the remote storage device 26 via a link 29. For example,
the transfer of data may be part of a data mirroring or replication
process that causes data on the remote storage device 26 to be
identical to the data on the storage device 24. Although only the
one link 29 is shown, it is possible to have additional links
between the storage devices 24, 26 and to have links between one or
both of the storage devices 24, 26 and other storage devices (not
shown). The storage device 24 may include a first plurality of
remote adapter units (RA's) 30a, 30b, 30c. The RA's 30a-30c may be
coupled to the link 29 and be similar to the HA 28, but are used to
transfer data between the storage devices 24, 26.
[0019] The storage device 24 may include one or more disks
(including solid state storage), each containing a different
portion of data stored on each of the storage device 24. FIG. 1
shows the storage device 24 having a plurality of disks 33a, 33b,
33c. The storage device (and/or remote storage device 26) may be
provided as a stand-alone device coupled to the host 22 as shown in
FIG. 1 or, alternatively, the storage device 24 (and/or remote
storage device 26) may be part of a storage area network (SAN) that
includes a plurality of other storage devices as well as routers,
network connections, etc. (not shown). The storage devices may be
coupled to a SAN fabric and/or be part of a SAN fabric. The system
described herein may be implemented using software, hardware,
and/or a combination of software and hardware where software may be
stored in a computer readable medium and executed by one or more
processors.
[0020] Each of the disks 33a-33c may be coupled to a corresponding
disk adapter unit (DA) 35a, 35b, 35c that provides data to a
corresponding one of the disks 33a-33c and receives data from a
corresponding one of the disks 33a-33c. An internal data path
exists between the DA's 35a-35c, the HA 28 and the RA's 30a-30c of
the storage device 24. Note that, in other embodiments, it is
possible for more than one disk to be serviced by a DA and that it
is possible for more than one DA to service a disk. The storage
device 24 may also include a global memory 37 that may be used to
facilitate data transferred between the DA's 35a-35c, the HA 28 and
the RA's 30a-30c. The memory 37 may contain tasks that are to be
performed by one or more of the DA's 35a-35c, the HA 28 and/or the
RA's 30a-30c, and may contain a cache for data fetched from one or
more of the disks 33a-33c.
[0021] The storage space in the storage device 24 that corresponds
to the disks 33a-33c may be subdivided into a plurality of volumes
or logical devices. The logical devices may or may not correspond
to the physical storage space of the disks 33a-33c. Thus, for
example, the disk 33a may contain a plurality of logical devices
or, alternatively, a single logical device could span both of the
disks 33a, 33b. Similarly, the storage space for the remote storage
device 26 may be subdivided into a plurality of volumes or logical
devices, where each of the logical devices may or may not
correspond to one or more disks of the remote storage device
26.
[0022] FIG. 2 is a schematic diagram 40 illustrating an embodiment
of the storage device 24 where each of a plurality of directors
42a-42n are coupled to the memory 37. Each of the directors 42a-42n
represents at least one of the HA 28, RAs 30a-30c, or DAs 35a-35c.
The diagram 40 also shows an optional communication module (CM) 44
that provides an alternative communication path between the
directors 42a-42n. Each of the directors 42a-42n may be coupled to
the CM 44 so that any one of the directors 42a-42n may send a
message and/or data to any other one of the directors 42a-42n
without needing to go through the memory 26. The CM 44 may be
implemented using conventional MUX/router technology where a
sending one of the directors 42a-42n provides an appropriate
address to cause a message and/or data to be received by an
intended receiving one of the directors 42a-42n. Some or all of the
functionality of the CM 44 may be implemented using one or more of
the directors 42a-42n so that, for example, the directors 42a-42n
may be interconnected directly with the interconnection
functionality being provided on each of the directors 42a-42n. In
addition, a sending one of the directors 42a-42n may be able to
broadcast a message to all of the other directors 42a-42n at the
same time.
[0023] In some embodiments, one or more of the directors 42a-42n
may have multiple processor systems thereon and thus may be able to
perform functions for multiple directors. In some embodiments, at
least one of the directors 42a-42n having multiple processor
systems thereon may simultaneously perform the functions of at
least two different types of directors (e.g., an HA and a DA).
Furthermore, in some embodiments, at least one of the directors
42a-42n having multiple processor systems thereon may
simultaneously perform the functions of at least one type of
director and perform other processing with the other processing
system. In addition, all or at least part of the global memory 37
may be provided on one or more of the directors 42a-42n and shared
with other ones of the directors 42a-42n. In an embodiment, the
features discussed in connection with the storage device 24 may be
provided as one or more director boards having CPUs, memory (e.g.,
DRAM, etc.) and interfaces with Input/Output (I/O) modules.
[0024] FIG. 3 is a schematic illustration showing a system 100 with
the host 22 and the data storage device 24 coupled to a cloud
service 110. The cloud service 110 may be coupled to the storage
device 24 using, for example, a conventional TCP/IP connection
therebetween, although other types of connections may be used. In
some instances, the cloud service 110 may also exchange data (e.g.,
control/status information) with the host 22 using, for example, a
TCP/IP connection. In other embodiments, the host 22 does not
communicate directly with the cloud service 110. The cloud service
110 may be a public commercially-available cloud storage, such as
the AWS cloud computing system provided by Amazon, the IBM Cloud,
etc. The cloud service 110 could also be implemented with one or
more private cloud services by an organization for use by members
only. The cloud service 110 could also be implemented using a
combination of one or more public cloud systems with one or more
private cloud systems. Generally, the cloud service 110 provides
on-demand service, broad network access, resource pooling, and
rapid elasticity or expansion.
[0025] The connection mechanism between the host 22 and the data
storage device 24 may include an Internet connection and/or
possibly some other types of connection(s). In an embodiment
herein, the connection mechanism may be directly incompatible with
a FICON connection on at least one end of the connection and thus
may rely on a FICON emulator (and/or other emulator(s)) for
providing data in an appropriate format. It is further noted that
where FICON emulation is being performed, the data storage device
24 may include or be coupled to a FICON emulator portion that may
send and receive data to and from the connection mechanism and also
emulates a Fibre Channel FCO physical layer for the benefit of the
data storage device 24. Thus, in a case involving emulation, both
the host 22 and the data storage device 24 may operate as if the
devices 22, 24 were communicating directly using a FICON hardware
connection.
[0026] In an embodiment, the system described herein may be used
with IBM's z High Performance FICON (zHPF) transport mode protocol
implementation. zHPF enhances z/Architecture and FICON interface
architecture to improve data transfer processing. In z/OS, standard
FICON architecture operates with the command mode protocol, and a
zHPF architecture operates with the transport mode protocol. zHPF
provides a Transport Control Word (TCW) that facilitates the
processing of an I/O request by the channel and the controller. The
TCW enables multiple channel commands to be sent to the controller
as a single entity (instead of being sent as separate commands as
in a FICON channel command word (CCW)). The channel no longer has
to process and keep track of each individual CCW. The channel
forwards a chain of commands to the controller for execution. zHPF
capable channels may support both FICON and zHPF protocols
simultaneously. For a more detailed discussion of zHPF, reference
is made, for example, to C. Cronin, "IBM System z10 I/O and High
Performance FICON for System z Channel Performance," Technical
paper, IBM Corporation, Jan. 28, 2009, 33 pp., which is
incorporated herein by reference.
[0027] It is possible to transfer a data set 112 (e.g., a volume, a
range of extents, etc.) to provide a copied data set 112' at the
cloud service 110. Conventionally, it is not acceptable to modify
the data set 112 while data is being replicated to the cloud
service 110 because doing so would make the copied data set 112'
inconsistent. However, in the system described herein, it is
possible for the host 22 to modify the data set 112 (i.e., write
data to the data set 112) on the storage device 24 while data is
being replicated from the data set 112 to the copied data set 112'.
In an embodiment herein, a version of the data set 112 that is
replicated to the copied data set 112' corresponds to a version of
the data set 112 at a time prior to when the replication operation
is initiated. That is, if replication is initiated at a time T,
and, during replication the host 22 writes data to the data set
112, the copied data set 112' will correspond to a state of the
data set 112 before the time T, irrespective of whatever data was
written by the host 22 to the data set 112 after the time T. This
is explained in more detail elsewhere herein.
[0028] Referring to FIG. 4, a diagram 400 illustrates data 402 from
the data set 112 along with metadata 404 and pool storage 406.
Accessing the data set 112 on the storage device 24 is performed
using the metadata 404 to determine a location of the data 402.
Using metadata to access underlying data on a storage device is
generally known. The metadata 404 includes pointers to the data 402
of the data set 112 so that, for example, if the storage device 22
(or another entity) accesses a portion of the data 402 of the data
set 112, the storage device 24 first accesses the metadata 404 to
determine a storage location (e.g., a physical location on one of
the disk drives 33a-33c) of the data 402 being accessed.
[0029] The storage pool 406 may include storage space that is not
generally accessible by the host 22 or any other external entity.
Rather, the storage pool 406 is accessible only by the storage
device 24 and is used to facilitate providing a snapshot of the
data set 112. In an embodiment herein, all of the pointers of the
metadata 404 initially point to only the data 402 for the data set
112. Following initiating a snapshot of the data set 112, the
metadata 404 and the storage pool 406 are used to maintain a point
in time version of the data set 112 corresponding to the data 402
of the data set 112 at the time of the snapshot. This is described
in more detail elsewhere herein and is also described in U.S. Pat.
No. 7,249,130 to Vishlitzky, et al., which is incorporated by
reference herein.
[0030] Referring to FIG. 5, a flow diagram 500 illustrates steps
performed in connection with replicating the data set 112 to the
cloud service 110. Processing begins at a first step 502 where a
snapshot is initiated. Initiating the snapshot at the step 502
causes subsequent data writes to the data set 112 by the host 22
(or by another entity) to be handled in a special manner, as
described in more detail elsewhere herein. Following the step 502
is a step 504 where data is transferred from the storage device 24
to the cloud service 110. Transferring the data at the step 504 is
discussed in more detail elsewhere herein. Following the step 504
is a step 506 where the snapshot is terminated. Following the step
506, processing is complete. Note that, following termination of
the snapshot at the step 506, subsequent writes to the data set 112
are not handled in any special manner.
[0031] Referring to FIG. 6, a flow diagram 600 illustrates
processing performed in connection with the step 504 of the flow
diagram 500, discussed above, where a data set 112 is transferred
from the storage device 24 to the cloud service 110. Processing
begins at a first step 602 where a pointer that iterates through
blocks (sections, portions) of the data of the data set 112 set is
initialized to point to the first block. Following the first step
602 is a test step 604 where it is determined if the iteration
pointer points past the end of the data of the data set 112. If so,
processing is complete. Otherwise, control transfers from the test
step 604 to a step 606 where an original version of a block of the
data set 112 is transferred to the cloud service 110. An original
version of a block of the data set 112 contains the data 402 that
existed at a time that the snapshot was initiated at the step 502,
discussed above. Obtaining the original version at the step 606 is
discussed in more detail elsewhere herein. Following the step 606
is a step 608 where the pointer that iterates through the blocks is
incremented. Following the step 608, control transfers back to the
step 604, discussed above, for another iteration.
[0032] Referring to FIG. 7, a flow diagram 700 illustrates
processing performed in connection with handling a write to the
data set 112 at the storage device 24. The embodiment illustrated
by the flow diagram 700 copies portions of the data 402 from the
data set 112 to the storage pool 406 and then overwrites the
portion of the data 402 in response to a write to the data set 112
after a snapshot is initiated. Processing begins at a first test
step 702 where it is determined if a snapshot has been initiated
(e.g., at the step 502 of the flow diagram 500, discussed above).
If not, then control transfers from the test step 702 to a step 704
where a conventional write operation is performed. Following the
step 704, processing is complete.
[0033] If it is determined at the test step 702 that a snapshot has
been initiated, then control transfers from the test step 702 to a
test step 706 where it is determined if a previous write operation
has already been performed to the block (section, portion) of the
data 402 after initiation of the snapshot. If not, then control
transfers from the test step 706 to a step 708 where a pointer in
the metadata 404 that points to the block of the data 402 is
adjusted to point to a block in the storage pool 406. Following the
step 708 is a step 712 where the relevant portion of the data 402
from the data set 112 (i.e., the portion being written) is copied
to the block in the data pool 406. Following the step 712 is a step
714 where the data 402 is overwritten with the new data. Note that
the step 714 is also reached directly from the test step 706 if it
is determined at the test step 706 that a previous write operation
has already been performed. Once the original block of the data 402
has been copied to the storage pool 406, subsequent writes to the
same block overwrite data at the same block. Following the step
714, processing is complete.
[0034] Note that, for the embodiment of FIG. 7, accessing an
original version of the data for the data set 112 at the step 606
includes accessing the metadata 404 to determine if an original
version of a particular block (portion, section) is either with the
data 402 (because no writes were performed following initiating a
snapshot) or with the data pool 406 (because at least one write was
performed following initiating a snapshot). Thus, a consistent
version of the data set 112 is replicated to the cloud service 110
while still allowing writes to be performed to the data set
112.
[0035] Referring to FIG. 8, a flow diagram 800 illustrates an
alternative embodiment of processing performed in connection with
handling a write to the data set 112 at the storage device 24. The
embodiment illustrated by the flow diagram 800 maintains (does not
modify) the data 402 from the data set 112 after a snapshot is
initiated while data written to the data set 112 after a snapshot
is initiated is copied to the storage pool 406. Processing begins
at a first test step 802 where it is determined if a snapshot has
been initiated (e.g., at the step 502 of the flow diagram 500,
discussed above). If not, then control transfers from the test step
802 to a step 804 where a conventional write operation is
performed. Following the step 804, processing is complete.
[0036] If it is determined at the test step 802 that a snapshot has
been initiated, then control transfers from the test step 802 to a
test step 806 where it is determined if a previous write operation
has already been performed to the block (section, portion) of the
data 402 after initiating the snapshot. If not, then control
transfers from the test step 806 to a step 808 where a pointer in
the metadata 404 is initialized to point to a block in the storage
pool 406. Following the step 808 is a step 812 where the data being
written is provided to the block in the data pool 406. Note that
the step 812 is also reached directly from the test step 806 if it
is determined at the test step 806 that a previous write operation
has already been performed after initiating the snapshot. After a
first write to a particular block, subsequent writes to the same
block overwrite data at the block in the storage pool 406.
Following the step 812, processing is complete.
[0037] Note that, for the embodiment of FIG. 8, accessing an
original version of the data for the data set 112 at the step 606
includes accessing only the data 402 because, by design, the data
402 is never modified after a snapshot is initiated. Thus, a
consistent version of the data set 112 is replicated to the cloud
service 110 while still allowing writes to be performed to the data
set 112.
[0038] Various embodiments discussed herein may be combined with
each other in appropriate combinations in connection with the
system described herein. Additionally, in some instances, the order
of steps in the flow diagrams, flowcharts and/or described flow
processing may be modified, where appropriate. Further, various
aspects of the system described herein may be implemented using
software, hardware, a combination of software and hardware and/or
other computer-implemented modules or devices having the described
features and performing the described functions. The system may
further include a display and/or other computer components for
providing a suitable interface with a user and/or with other
computers.
[0039] Software implementations of the system described herein may
include executable code that is stored in a non-transitory
computer-readable medium and executed by one or more processors.
The computer-readable medium may include volatile memory and/or
non-volatile memory, and may include, for example, a computer hard
drive, ROM, RAM, flash memory, portable computer storage media such
as a CD-ROM, a DVD-ROM, an SD card, a flash drive or other drive
with, for example, a universal serial bus (USB) interface, and/or
any other appropriate tangible or non-transitory computer-readable
medium or computer memory on which executable code may be stored
and executed by a processor. The system described herein may be
used in connection with any appropriate operating system.
[0040] Other embodiments of the invention will be apparent to those
skilled in the art from a consideration of the specification or
practice of the invention disclosed herein. It is intended that the
specification and examples be considered as exemplary only, with
the true scope and spirit of the invention being indicated by the
following claims.
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